Lightweight motorized wheelchair

ABSTRACT

A wheelchair having a seat and a plurality of wheels for rolling the wheelchair along a ground surface. A plurality of legs are provided for supporting the seat. Each of the legs is positioned between the seat and one of the wheels. A plurality of struts are also provided. The seat bottom and seat back are pivotally coupled to the seat bottom. The seat back is movable between a folded position and an unfolded position. An actuator for providing at least one actuator output signal in response to movement of the actuator by a user of the device is also provided.

This application is a continuation of U.S. Ser. No. 09/150,652 filedSep. 10, 1998, U.S. Pat. No. 6,183,002.

FIELD OF THE INVENTION

This invention relates generally to wheelchairs. More particularly, thisinvention relates to motorized wheelchairs that are lightweight,foldable and portable.

BACKGROUND

The current mobility assistance market is served by over 450 models ofmobility aids produced by more than 150 manufacturers. The fourcategories of mobility aids currently available include: (1) standardwheelchairs (manual propulsion); (2) ultralight wheelchairs (manualpropulsion); (3) three and four wheel scooters (powered propulsion); and(4) powered wheelchairs. Each of these categories of mobility aids arediscussed below.

Standard wheelchairs are the conventional, folding wheelchairs which canbe seen in hospitals, airports, and shopping malls. They typically comein two models: self propelled, with large wheels which a passenger usesto propel themselves, and “Attendant” models, which have smaller wheelsand are meant to be pushed by another person. Both types will typicallyfold sideways to make transport easier. Standard wheelchairs aretypically priced low enough such that health insurance reimbursement iseasily obtained for mid-range models based on a physician'sprescription. Key shortcomings of standard wheelchairs include theirunattractive, orthopedic product designs, and the fact that eitherphysical exertion or an attendant is required to propel the chair.

Ultralight wheelchairs, the newest, most visible products, are currentlyreceiving strong publicity. They are built out of exotic alloys andemploy radical new designs in order to be quick and agile. Their reducedweight makes them easy to use and lift, but the frames will nottypically fold. They typically are more expensive than standardwheelchairs, and are targeted toward younger, more active users. As aresult of their higher cost, health insurance reimbursement is typicallyavailable only for an individual with a full-time need and only with aphysician's prescription. Key shortcomings of the ultralight wheelchairsinclude the fact that manual exertion is required to move the chair, theorthopedic nature of the design, and the high price of such chairslimits their availability as a secondary or discretionary aid purchase.

Scooters are built in three and four wheel configurations and comeclosest to the industry's notion of a “consumer product,” mitigating, toa large degree, the “handicapped” stigma associated with wheelchairs.Scooters are designed with thorough attention to aesthetics, areattractive in appearance, and perceived as fun, liberating andfree-spirited in use. They are robust enough to function incross-country and non-access-ready environments. While built to servethe needs of severely disabled individuals able to obtain healthinsurance reimbursement, scooters are also purchased, on anon-reimbursed basis, by individuals who have mobility difficultieswhich are not severe enough to qualify for reimbursement.

The most widely sold scooter models cost between three and five timesthe cost of standard wheelchairs, and weigh around 90 pounds withouttheir batteries. Obtaining health insurance reimbursement for scooters(or any other powered mobility aid) is much more difficult than formanual wheelchairs; it typically requires an acute need (such asfull-time impairment), several physicians' prescriptions, and ongoingand consistent follow up by physical therapists or equipment dealers.Key shortcomings of scooters include their high prices, limiting theirdiscretionary purchase acceptability, their large size, making themcumbersome and obtrusive when used indoors or in social situations, andtheir heavy weight, making scooters difficult to transport, typicallyrequiring disassembly or a van to be transported for use elsewhere.

Powered wheelchairs are becoming more sophisticated and robust with eachdesign iteration. They are currently increasing in weight and cost asthe frame designs, mechanicals, and electronics increase in complexity.Since they are designed exclusively for the needs of severely disabledindividuals, they are heavy-duty medical appliances, which can handle awide variety of non-access-ready environments and can overcomesignificant environmental obstacles. They are currently purchased almostexclusively with health insurance reimbursement, often require the closeinvolvement of a team of healthcare professionals (physicians, physicaltherapists, wheelchair specialists) to fulfill prescriptive requirementsand conduct a customized “fitting” of the wheelchair, and are generallyused by individuals with only the greatest degree of impairment ordisability. As a powered mobility aid, the procedures and qualificationsfor health insurance reimbursement are similar in nature, but moreextensive, than those required for scooters. Powered wheelchairs willtypically cost between four to eight times the cost of standardwheelchairs, and weigh between 80 and 150 pounds (without batteries).Weight has not typically been a consideration for manufacturers ofpowered wheelchairs, since severely disabled users will normally havemodified their lifestyles, transportation means and living environmentsto accommodate their needs. The key shortcomings of powered wheelchairsinclude their high price, as they are specialized medical applicants,their heavy weight and large sizes which make them cumbersome totransport, and their unattractive, orthopedic appearance.

Each of the products discussed above is, by and large, derived from thehealthcare industry. Such products are largely medical and orthopedicappliances and, because of their cost, appearance, and cumbersomeness,are most suited to individuals with acute mobility difficulties whorequire full time mobility assistance. They were designed largely forfunctional use following a trauma and as such are (i) designed for usein all environments (including those that are not handicapaccess-ready); (ii) unappealing, heavy steel and chrome orthopedicappliances, (iii) heavy and unwieldy which make them difficult orimpossible to transport; and (iv) large obtrusive and ungainly inoperation.

A final issue surrounding current products relates to their prescriptivenature and the difficulty of obtaining health insurance reimbursement.Standard wheelchairs are easily reimbursed based on a generallyprescribed need. Ultralight wheelchairs can be reimbursed if the need isfull-time or more specialized and this need is reflected in theprescription. For powered aid reimbursement, either scooters orwheelchairs, the difficulty increases dramatically. Often severalphysicians will need to support the prescription process, and physicaltherapists or equipment specialists will need to follow up with theagencies. In all cases, health insurance will only reimburse the cost ofa single mobility aid. The costs of any secondary or discretionary aidsthat may be desired (such as a light wheelchair for transport and use inplace of a scooter) are borne solely by the customer.

There are several common attributes that wheelchair and scooter usersdesire. Each of the products described above meet some, but not all, ofthese criteria. As Table I below shows, consumers are forced to makesubstantial compromises when selecting from one of the currentlyavailable products. A “WA” in the table below indicates that thecriteria is “well-addressed” by the product, and a “PA” indicates thatthe criteria is “partially addressed” by the product.

TABLE I Current Mobility Aids & Characteristics Easy-To- Non- AllAffordable Transportable Comfortable Use orthopedic Unobtrusive PoweredTerrain Standard WA WA WA PA Wheelchairs Ultralight WA WA PA WA PAWheelchairs Powered WA PA PA Wheelchairs Scooters WA PA WA PA PA

The present invention is designed to satisfy the needs of individualswho are not dependent on a full-time mobility aid; rather it is targetedtowards those individuals who experience pain, difficulty or tire easilywhen walking. As such, it is an object of the present invention toprovide a mobility aid for part time discretionary assistance. That is,for use by individuals who are able to walk unaided or with somemobility assistance, but experience pain or tiredness when conductingtheir daily routines around their home, work, community or shoppingcenters.

It is a further object of the present invention to provide a mobilityaid with an unobtrusive and appealing design which rigorously avoids thetraditional “orthopedic” design of conventional wheelchairs, and alsoavoids the stigma associated with their use. Thus, it is an object ofthe present invention to provide a mobility aid that can be used byanyone without engendering, to either the user or onlookers, a sense ofbeing handicapped.

It is a further object of the present invention to provide a mobilityaid that folds compactly, is lightweight and highly transportable. Thus,as discussed more fully below, the present invention incorporates aframe that is sturdy and rigid when in use, but which can be quickly andcompactly folded for transport. Other powered wheelchairs will collapseto a limited degree, but the present invention folds to a small, flatpackage, weighing less than 25 pounds, which is easily lifted into a cartrunk or back seat.

It is a still further object of the present invention to provide abattery powered mobility aid that is highly affordable. Thus, asdiscussed more fully below, the present invention has an overall lowweight and power management electronics that can be driven effectivelywith a single, small battery (approximately 10 pounds).

It is a still further object of the present invention to provide apowered mobility aid which is easy for a user to control and maneuverduring use of the device.

These and other objects and advantages of the invention will become morefully apparent from the description and claims which follow or may belearned by the practice of the invention.

SUMMARY OF THE INVENTION

The present invention is directed to a wheelchair having a seat and aplurality of wheels for rolling the wheelchair along a ground surface. Aplurality of legs are provided for supporting the seat. Each of the legsis positioned between the seat and one of the wheels. A plurality ofstruts are also provided. Each of the struts couples a first of the legsto a second of the legs. Each of the legs bears only compressive forcein supporting the seat, and each of the struts bears only tensile force.

In accordance with a further aspect, the present invention is directedto a foldable wheelchair formed from a seat bottom and a seat backpivotally coupled to the seat bottom. The seat back is movable between afolded position and an unfolded position. The seat bottom has a back endformed from a first curved shape, and the seat back has a bottom endformed from a second curved shape. The first curved shape of the seatbottom is sized to mate with the second curved shape of the seat backwhen the seat back is in the unfolded position.

In accordance with a still further aspect, the present invention isdirected to a portable mobility device that includes an actuator forproviding at least one actuator output signal in response to movement ofthe actuator by a user of the device. The actuator is movable over arange of positions, the range of positions being bounded by a minimumspeed actuator position at a first end of the range and a maximum speedactuator position at an opposite end of the range. The range ofpositions includes a mid-point actuator position located on the rangeexactly midway between the minimum speed actuator position and themaximum speed actuator position. The actuator output signal has amagnitude that is linearly related to the position of the actuator onthe range of positions. A non-linear amplifier, responsive to theactuator output signal, is provided for outputting a motor controlsignal. The motor control signal has a minimum value when the actuatoris located at the minimum speed actuator position, a maximum value whenthe actuator is located at the maximum speed actuator position, and themotor control signal has its median value when the actuator is locatedbetween the mid-point speed actuator position and the maximum speedactuator position. The non-linear amplifier thus causes the speed of thedevice to change least drastically in response to variations in theactuator position when the actuator is closest to its minimum speedposition, and the non-linear amplifier causes the speed of the device tochange most drastically in response to variations in the actuatorposition when the actuator is closest to its maximum speed position.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the manner in which the above-recited and other advantagesand objects of the invention are obtained and can be appreciated, a moreparticular description of the invention briefly described above will berendered by reference to a specific embodiment thereof which isillustrated in the appended drawings. Understanding that these drawingsdepict only a typical embodiment of the invention and are not thereforeto be considered limiting of its scope, the invention and the presentlyunderstood best mode thereof will be described and explained withadditional specificity and detail through the use of the accompanyingdrawings.

FIG. 1 is a side view of a lightweight, foldable, and motorizedwheelchair, in accordance with a preferred embodiment of the presentinvention.

FIG. 2 is an enlarged view showing the connection between a seat supportmember and the central strut member of the wheelchair shown in FIG. 1.

FIG. 3 is an enlarged view of a portion of a seat support member of thewheelchair shown in FIG. 1.

FIG. 4 is a front view of the wheelchair shown in FIG. 1.

FIG. 5 is a partial isometric view of the wheelchair shown in FIG. 1.

FIG. 6A is an exploded view of the seat bottom and seat back of thewheelchair shown in FIG. 1, showing a mating curvature used forconnecting the seat bottom and seat back.

FIG. 6B is a rear view of the seat back shown in FIG. 6A.

FIG. 6C shows the seat bottom and seat back of the present invention intheir fully-unfolded position.

FIG. 6D is a cross-sectional view of 6C, and shows the seat bottom andseat back of the present invention in their fully-unfolded position.

FIG. 6E is a cross-sectional view of the seat bottom and seat back ofthe present invention shown in their partially folded position.

FIG. 7A is a block diagram showing the operation of controllers fordriving the motors of the wheelchair shown in FIG. 1, in accordance witha preferred embodiment of the present invention.

FIG. 7B is a diagram showing the linear relationship between theactuation angle imparted (by a user) to a joystick and the magnitude ofthe signals output by the joystick in response to such actuation angle.

FIG. 7C is a diagram showing the non-linear relationship between theactuation angle imparted (by a user) to a joystick and the magnitude ofthe signals output by an amplifier in response to such actuation angle,in accordance with a preferred embodiment of the present invention.

FIG. 8 is a side view showing the wheelchair of FIG. 1 in apartially-folded position.

FIG. 9 is a side view showing the wheelchair of FIG. 1 in a fully-foldedposition.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIGS. 1-5, there are shown various views of alightweight, foldable, and motorized wheelchair 100, in accordance witha preferred embodiment of the present invention. Wheelchair 100 isformed of a seat bottom 10 and a seat back 20. Seat back 20 is pivotallycoupled to seat bottom 10 at pivot point P, and is pivotable along arcA. Front wheels 72, 74 and rear wheels 76, 78 are provided for rollingthe wheelchair along a ground surface S. Legs 32, 34, 36 and 38 areprovided for supporting the seat bottom 10 (and a user) during operationof wheelchair 100. Thus, each one of the legs 32, 34, 36, and 38 ispreferably positioned between the seat bottom 10 and a corresponding oneof the wheels 72, 74, 76 and 78. Struts 52, 54, 56, 58, 60 and 62 areprovided for connecting selected pairs of legs 32, 34, 36 and 38 to oneand other. As explained more fully below, during operation of wheelchair100 when a user is seated on seat bottom 10, legs 32, 34, 36 and 38 bearonly compressive force in supporting seat bottom 10, and each of thestruts 52, 54, 56, 58, 60 and 62 bears only tensile force. Thisarrangement of legs and struts provides a highly stable, lightweight andfoldable support structure for seat bottom 10.

As shown in FIGS. 1, 4 and 5, each of the legs 32, 34, 36 and 38 ispreferably positioned at an acute angle with respect to the groundsurface S. In the preferred embodiment, legs 32 and 34 are positioned atangle of about 67 to 72 degrees with respect to surface S, and legs 36and 38 are positioned at an angle of about 57 to 62 degrees with respectto surface S. The upper ends of legs 32 and 36 are pivotally coupled toseat support bar 40 which, in turn, is rigidly coupled to seat bottom10. Similarly, the upper ends of legs 34 and 38 are pivotally coupled toseat support bar 44 which, in turn, is rigidly coupled to seat bottom10. Each of the seat support bars 40, 44 includes an internal track 42for guiding and restraining the upper ends of legs 36 and 38. Whenwheelchair 100 is in its unfolded position (shown in FIGS. 1, 2, 4 and5), the upper end of each leg 36, 38 is locked in position at one end ofa track 42 by a pivoting locking bar 65. During the folding ofwheelchair 100, each locking bar 65 is pivoted about a point L (bydepressing one end of the bar 65) in order to release the upper ends oflegs 36, 38. Once the legs 36, 38 are so released, the upper ends oflegs 36, 38 are free to slide along tracks 42, thus facilitating thefolding of the wheelchair 100 as shown in FIG. 5.

As shown more particularly in FIGS. 4 and 5, strut 52 rigidly connectsthe top end of leg 34 to the bottom end of leg 32, and strut 54 rigidlyconnects the top end of leg 32 to the bottom end of leg 34. Similarly,strut 58 rigidly connects the top end of leg 38 to the bottom end of leg36 and strut 56 rigidly connects the top end of leg 36 to the bottom endof leg 38. Strut 60 is pivotally connected at one of its ends to the topend of leg 32 and is pivotally connected at its other end to the bottomend of leg 36. Similarly, strut 62 is pivotally connected at one of itsends to the top end of leg 34 and is pivotally connected at its otherend to the bottom end of leg 38.

Referring now to FIGS. 1, 4 and 5, cross-beam 66 is provided for rigidlycoupling the bottom end of leg 32 to the bottom end of leg 34. A furthercross-beam 68 is provided for rigidly coupling seat support member 40 toseat support member 44. A foldable strut 64 spans between cross-beam 66and cross-beam 68. Foldable strut 64 includes a pair of angled members64 a, each of which is rigidly connected to cross-beam 66. Foldablestrut 64 also includes a member 64 b which is pivotally mounted tocross-beam 68. During operation (use) of wheelchair 100 by a user,angled members 64 a are rigidly coupled to member 64 b by a releasablelocking means 64 d. During the folding of wheelchair 100, locking means64 d is released, allowing strut 64 to fold about its midpoint 64 c.

In the preferred embodiment, a foot rest support member 84 is rigidlyaffixed to cross-beam 66. A pair of foot supports 82 are pivotallymounted to member 84. During operation of the wheelchair 100, footsupports 82 are preferably placed in their unfolded position (shown inFIG. 1). During folding of the chair, the upper ends of foot supports 82are pivoted towards support member 84 (as shown in FIG. 9). Adjustmentscrews (not shown) are preferably provided for adjusting the height ofthe foot supports 82 in order to customize wheelchair 100 for users ofdifferent heights.

The legs, struts, cross-beams and support members discussed above arepreferably formed from a material that is lightweight and strong. In aparticularly preferred embodiment, where the legs, struts, cross-beamsand support members are formed of aircraft aluminum, high tensile steel,or fiber composite material, the total weight of wheelchair 100 (notincluding the weight of batteries) may be made less than 25 pounds.

Referring now to FIGS. 6A-6E, there are shown several views illustratinga mating curvature used for connecting the seat bottom 10 and seat back20 of wheelchair 100. The seat bottom 10 has a back end 12 formed from afirst curved shape 14. The seat back 20 is pivotally coupled to the seatbottom 10 as described above, and is movable between folded positions(shown in FIGS. 6E, 8 and 9) and an unfolded position (shown in FIGS. 1,4, 6C and 6D). The seat back 20 has a bottom end 22 formed from a secondcurved shape 24. The curved shape 14 of the seat bottom 10 is sized tomate flush with the curved shape 24 of the seat back 20 when the seatback is in its unfolded position. As shown by a comparison of FIGS. 1and 8, the seat back 20 is oriented at a minimum angle (approximately 0degrees) with respect to the seat bottom 10 when the seat back is in itsfolded position, and the seat back 20 is oriented at a maximum angle(approximately 100 degrees) with respect to the seat bottom 10 when theseat back 20 is in its unfolded position. During operation of thewheelchair 100, when a user is positioned seated on seat bottom 10 andleaning against seat back 20, seat back 20 is preferably restrained frompivoting or extending beyond the maximum angle solely by the back end 12of the seat bottom 10. In other words, the mating curvature formedbetween seat bottom 10 and seat back 20 preferably forms the sole stoprestraining backward movement of the seat back 20 (beyond the limit ofarc A) when a user sits in seat bottom 10 and leans against seat back20. By forming this stop solely from the mating curvature between theseat bottom 10 and the seat back 20, the number of components inwheelchair 100 is minimized, thereby reducing the final weight of thewheelchair.

The seat bottom 10 and the seat back 20 discussed above are preferablyformed from a material that is lightweight and strong. In a particularlypreferred embodiment, the seat bottom 10 and the seat back 20 are formedof fiber glass reinforced plastic.

Referring now to FIG. 7A, there is shown a block diagram illustratingthe operation of two controllers for driving independent motors 90 and92 of the wheelchair shown in FIG. 1, in accordance with a preferredembodiment of the present invention. Motor 90 is preferably coupled toand drives rear wheel 76, and motor 92 is preferably coupled to anddrives rear wheel 78. Joystick actuator 96 is a standard joystick and,as such, it provides three output signals namely, an X(+/−) signal, aY(+/−) signal, and a reference signal. The X(+/−) signal and Y(+/−)signal represent the x-y coordinates on a Cartesian plane whichcorrespond to the “angle” and “direction” at which the joystick ispositioned at any given moment in time. When no force is applied tojoystick actuator 96, the joystick is preferably aligned in a verticalposition such that the joystick is straight-up-and-down. When thejoystick is aligned in this straight-up-and-down position, the “angle”of the joystick relative to the vertical axis is zero. As a user impartsan actuation force to the joystick, the angle between this vertical axisand joystick becomes positive and, as explained more fully below, thevelocity of the wheelchair increases (non-linearly) as the angle betweenthe vertical axis and the joystick increases. Joystick 96 can thus bepositioned by a user at any location within a range of possible anglesin order to vary/control the speed of the wheelchair. The range ofangles typically varies from a minimum of angle of 0 zero degrees (whenthe joystick is straight-up-and-down) and a maximum angle of about 30degrees (when the joystick is tilted as far as it will go away from thevertical axis). The “angle” at which the joystick is positioned relativeto the vertical axis at any given moment in time corresponds linearly tothe Euclidean magnitude represented by the X(+/−) and Y(+/−) signalsoutput by the joystick 96. Similarly, the “direction” (along a 360degree azimuth) toward which the tilted joystick points at any givenmoment in time corresponds to the Euclidean angle represented by theinverse cosine of the X(+/−) and Y(+/−) signals output by the joystick96. A standard joystick actuator, such as that manufactured by CHProducts, Vista, Calif., under Part #100-800 IJ 1DM, may be used toimplement joystick actuator 96.

Referring still to FIG. 7A, the X(+/−) and Y(+/−) signals describedabove, together with a power signal from battery 95 are provided to botha right motor controller (for driving motor 92) and a separate leftmotor controller (for driving motor 90). Initially, the X(+/−) andY(+/−) signals are provided to a forward/reverse (f/r) detector 110 ineach motor controller. Based on the Euclidean angle represented by theinverse cosine of the X(+/−) and Y(+/−) signals, the f/r detector 110 inthe right motor controller determines whether motor 92 should move inthe forward or reverse direction. Similarly, based on the Euclideanangle represented by the inverse cosine of the X(+/−) and Y(+/−)signals, the f/r detector 110 in the left motor controller determineswhether motor 90 should move in the forward or reverse direction. Theoutput of each fir detector 110 is supplied to a corresponding f/rswitch 120, which in turn functions to bias the output of an amplifier130. As mentioned above, the Euclidean magnitude represented by theX(+/−) and Y(+/−) signals output by the joystick 96 corresponds linearlyto the “angle” at which the joystick is positioned relative to thevertical axis at any given moment in time. Thus, as shown by the graphshown in FIG. 7B, the power level of the X(+/−) and Y(+/−) signalsoutput by joystick actuator 96 varies linearly from a zero power levelwhen the joystick is in its purely vertical position to a maximum 100%power level when the joystick is tilted as far as it will go away fromthe vertical axis.

As shown particularly in FIG. 7C, each non-linear amplifier 130 outputsa voltage that is related non-linearly to the power level of the X(+/−)and Y(+/−) signals output by joystick actuator 96. In the preferredembodiment shown in FIG. 7C, where the joystick angle may vary between aminimum angle of zero degrees and a maximum angle of 30 degrees, thevoltage output by amplifier 130 is significantly less than 50% ofmaximum (and preferably only about 30% of the maximum) when the joystickis positioned 15 degrees from the vertical (i.e., when the joystick ishalf-way between its minimum angle of zero degrees and its maximum angleof 30 degrees.) The non-linear amplifiers 130 thus cause the speed ofthe motors 90, 92 to change least drastically in response to variationsin the joystick angle when the joystick is closest to its purelyvertical angle, and the non-linear amplifiers 130 cause the speed of thedevice to change most drastically in response to variations in thejoystick angle when the joystick is tilted as far as it will go awayfrom the vertical axis. As a result of the use of non-linear amplifiers130 having response curves such as that shown in FIG. 7C, it is believedthat a user of the present mobility device is better able to control andmaneuver the device, because the user has finer control of thewheelchair at lower speeds.

Referring again to FIG. 7A, the output of each non-linear amplifier 130is provided to a pulse-width (PW) modulator 140. Each PW modulator 140is coupled to an oscillator having a frequency of about 15 Khz to 20Khz. In response to the voltage output by an amplifier 130, each PWmodulator 140 produces a pulse-width modulated signal. The width of thepulses in this signal is linearly related to the level of the voltagesignal provided to the PW modulator 140 by an amplifier 130. Thepulse-width modulated signal output by modulator 140 is provided to amotor driver 150.

The output of each PW Modulator 140 is also provided to a zero-drivedetector 160. Each zero-drive detector 160 monitors the signal output bya PW Modulator 140 to determine when the PW Modulator output signal hasa zero duty cycle. When the PW Modulator output signal has a zero dutycycle, this corresponds to a state when the joystick actuator 96 is inits purely vertical position and no force is being applied to thejoystick by a user. When the joystick 96 reaches this purely verticalposition, it is desirable for the wheelchair 100 to come to a stop assoon as is comfortably possible and for the wheelchair to remain in astopped position thereafter until the user moves the joystick 96 fromits purely vertical position. Accordingly, when a zero-drive detector160 detects that the PW Modulator output signal duty cycle is zero, thezero-drive detector 160 sends a signal to a brake circuit 170. Eachbrake circuit 170 functions to shunt the output of one of the motors 90,92, thereby resulting in dynamic braking action.

A standard gel lead acid battery, such as that manufactured byYuasa-Exide under model number NPG18-12 may be used to implement battery95. Battery 95 is preferably stored in battery case 94 during operationof wheelchair 100.

Furthermore, it is to be understood that although the present inventionhas been described with reference to a preferred embodiment, variousmodifications, known to those skilled in the art, may be made to thestructures and process steps presented herein without departing from theinvention as recited in the several claims appended hereto.

What is claimed is:
 1. A powered mobility aid comprising a seat having atop surface and a bottom surface and a seat back flexibly engagedtherewith, a foldable support frame having a plurality of wheels fixedto the seat, and a power source engaged with at least two of said wheelsfor applying a driving force to said wheels, wherein said foldablesupport frame includes: two track members positioned in a parallel andspaced relationship on the bottom surface of said seat, each trackmember extending from a point proximate said seat back toward the frontedge of the seat; two front legs, each front leg pivotally engaged withthe bottom surface of said seat, a front cross-beam extending betweenand fixed to said two front legs at a location spaced from said seat andproximate the distal ends of said front legs, two of said wheels eachbeing attached to said front cross beam and front leg combinationproximate the respective distal ends of each of said front legs, atleast one front reinforcing member fixed between said two front legs;two rear legs, each rear leg engaged with a respective track member andbeing slidable in said respective track member, two of said wheels eachbeing attached respectively proximate the distal end of each of said tworear legs, at least one rear reinforcing member fixed between said tworear legs; at least one side reinforcing member located on each side ofsaid support frame; a locking member extending from the bottom surfaceof said seat and to said front cross beam, said locking member beingengaged and locked when said frame is in a fully extended position andalso when said frame is in a completely folded position; and tracklocking members for locking said rear legs in position on said trackswhen said frame is fully extended.
 2. The powered mobility aid of claim1 further including a foot rest member proximate said front cross beam.3. The powered mobility aid of claim 2 wherein said foot rest memberincludes at least one support member pivotally engaged to fold betweenan open position to receive a user's feet and a closed position forstorage.
 4. The powered mobility aid of claim 1 wherein said powersource includes a battery pack and two electric motors, one motorengaged with each rear wheel respectively and a control stick incommunication with said battery pack and each electric motor forindependently operating each of said motors to drive and steer thepowered mobility aid.
 5. The powered mobility aid of claim 4 whereinsaid rear wheels are fixed in one operable position and said frontwheels each rotate 360°.
 6. The powered mobility aid of claim 1 whereinsaid power source includes a battery pack and two electric motors, onemotor engaged with each front wheel respectively and a control stick incommunication with said battery pack and each electric motor forindependently operating each of said motors to drive and steer thepowered mobility aid.
 7. The powered mobility aid of claim 6 whereinsaid front wheels are fixed in one operable position and said rearwheels each rotate 360°.
 8. The powered mobility aid of claim 1 whereinsaid track members are integrally formed with the bottom surface of saidseat.
 9. The powered mobility aid of claim 1 wherein each of said frontlegs is engaged with a respective track member and slidable in saidrespective track member and said rear legs are each pivotally engagedwith the bottom surface of said seat.
 10. The powered mobility aid ofclaim 9 further including a foot rest member proximate said front crossbeam.
 11. The powered mobility aid of claim 10 wherein said foot restmember includes at least one support member pivotally engaged to foldbetween an open position to receive a user's feet and a closed positionfor storage.
 12. The powered mobility aid of claim 9 wherein said powersource includes a battery pack and two electric motors, one motorengaged with each rear wheel respectively and a control stick incommunication with said battery pack and each electric motor forindependently operating each of said motors to drive and steer thepowered mobility aid.
 13. The powered mobility aid of claim 12 whereinsaid rear wheels are fixed in one operable position and said frontwheels each rotate 360°.
 14. The powered mobility aid of claim 9 whereinsaid power source includes a battery pack and two electric motors, onemotor engaged with each front wheel respectively and a control stick incommunication with said battery pack and each electric motor forindependently operating each of said motors to drive and steer thepowered mobility aid.
 15. The powered mobility aid of claim 14 whereinsaid front wheels are fixed in one operable position and said rearwheels each rotate 360°.
 16. The powered mobility aid of claim 9 whereinsaid track members are integrally formed with the bottom surface of saidseat.